CNS - Clinical Anatomy of the Eye Flashcards
1
Q
Explain the eye position in predatory species
A
Frontal/forward facing to allow for depth perception whilst hunting/binocular vision
2
Q
Explain the eye position in prey species
A
High up on head Lateral aspect (side of head) Greater range of vision - allows scanning of environment
3
Q
Where is a rabbits (or a horses) blind spot?
A
Right in front of it’s mouth/teeth. Need to be aware of this for examination
4
Q
How does the orbit of the eye differ between predatory and prey species e.g dog, cow, and horse?
A
In predators there is an incomplete bony orbit with the orbital ligament completing the orbit - allows further movement of the mandible and therefore allows the jaw to open wider.
In prey there is a complete bony orbit
- in cattle this is formed by zygomatic process of the frontal bone and frontal process of the zygomatic bone
- in horses this is formed by zygomatic processes of the frontal bone and temporal bone, and the frontal process of the zygomatic bone
5
Q
What are the layers of orbital fascia?
A
Periorbita - periosteum/lining of the bone
Fascia bulbi - loose connective tissue. lines the sclera. lines outside of eyeball caudally. stops at junction between cornea and sclera. overlain by conjunctiva at the front
fascial sheaths of extraoccular muscles
6
Q
Name the 7 extraocular muscles
A
Dorsal Rectus Lateral Rectus Ventral Rectus Medial Rectus Ventral Oblique Dorsal Oblique Retractor Bulbi
7
Q
Which extraocular muscles are innervated by the occulomotor nerve (CNIII)?
A
Dorsal Rectus, Ventral Rectus, Medial Rectus, Ventral Oblique
8
Q
Which extraocular muscles are innervated by the trochlear nerve (CNIV)?
A
Dorsal Oblique
9
Q
Which extraocular muscles are innervated by the abducens nerve (CNVI)?
A
Lateral Rectus, Retractor Bulbi
10
Q
What is strabismus?
A
Strabismus, more commonly known as cross-eyed or wall-eyed, is a vision condition in which an animal can not align both eyes simultaneously under normal conditions. One or both of the eyes may turn in, out, up or down
11
Q
Functions of the eyelids
A
Removes foreign material Protects eye Blocks out light Spreads tear film Clears things towards drainage ducts
12
Q
What is the purpose of the tarsal glands?
A
Forms the lipid component of the tear film
13
Q
What is the purpose of the lipid component of the tear film?
A
helps to reduce spillage onto face
helps stop evaporation
14
Q
What is the tarsal plate and what is it’s function?
A
cartilage surrounding the tarsal glands. keeps the eyelid structure from going floppy
15
Q
What are the muscles responsible for closing the eye?
A
orbicularis oculi (sphincter muscle surround the eye)
16
Q
What are the muscles responsible for opening the eye?
A
Levator palpebris superioris (opens eye) and levator anguli oculi (lifts up side of eyelid)
17
Q
What is the motor innervation of the eyelid?
A
CN VII (Facial Nerve) - Levator anguli oculi and Orbicularis oculi CN III (Occulomotor Nerve) - Levator palpebrae superioris Sympathetic NS innervation of smooth muscle
18
Q
What is the sensory innervation of the eyelid?
A
CN V (Trigeminal Nerve) - opthalmic and maxillary branches
19
Q
Which regions of the eyelid are innervated by the opthalmic and maxillary trigeminal nerve branches?
A
Opthalmic - Most of upper eyelid, and medial lower eyelid
Maxillary - Most of lower eyelid, and lateral upper eyelid
20
Q
Which species have a lacrimal caruncle?
A
Horses and human
21
Q
How do the eyelids and sclera differ between and horse and a cat?
A
Cat - eyelid held tight to the globe. Very little sclera visible, and is usually white?
Horse - loose “loopy” eyelids. Lots of sclera visible but often pigmented. Very wide palpebral fissure
22
Q
What type of dogs are most susceptible to palpebral abnormalities?
A
Brachycephalic
23
Q
What is entropion?
A
Rolling in of the eyelid resulting in hair rubbing on the cornea.
Overly long eyelid often the cause. Slice off loose skin for surgery
24
Q
What is ectropion?
A
Overlong eyelid so folding out.
Common in bloodhounds, mastiffs etc
Unable to sweep debris or tear film
Less catastrophic than entropion
25
What is a diamond eye?
Both entropion and ectropion (entropion laterally and ectropion medially)
26
What crucial cell type does the conjunctiva contain?
Goblet cells - mucous secretory cells
| Also lots of lymphoid tissues - plentiful follicles in back of 3rd eyelid
27
What are the three types of conjunctiva, and what does each type cover/line?
Palpebral conjunctiva - only lines in front of the eyeball/inside of eyelid
Nictitating conjunctiva - covers the 3rd eyelid
Bulbar conjunctiva - covers the sclera
28
What is the ventral fornix?
Infolding of conjunctiva - contains the 3rd eyelid AKA the nictitating membrane
29
What are the three components of the tear film?
Aqueous (NOT AQUEOUS HUMOUR!!!)
Lipid
Mucous
30
What can damage to the 3rd eyelid result in?
Dry eye
31
The leading edge of the 3rd eyelid...
...is supported by T shaped cartilage.
...must be firmly and consistently in contact with the eye
...is supported an supplied by the gland of the 3rd eyelid
32
What is a cherry eye?
Prolapsed gland of the 3rd eyelid over the leading edge of the 3rd eyelid. The gland is trapped there by the tightening of the leading edge.
Can reoccur. French bulldogs are particularly prone
33
How would you surgically treat a cherry eye?
Make pocket, push gland into pocket, suture pocket shut.
If prolapsed due to tumour, you would cut the prolapsed gland off but the animal will require subsequent treatment for dry eyes for the rest of it's life
34
What is the function of each part of the tear film and where is it produced?
Aqueous layer - from lacrimal and 3rd eyelid gland (2/3 lacrimal 1/3 eyelid).
- lubrication, protection and nutrition of corneal, limbal and conjunctival epithelium (cornea is avascular so tear film is necessary)
Mucin layer - from conjunctival goblet cells
- mixes with and stabilises aqueous layer
Lipid layer - from Meibomian/tarsal glands
- reduces evaporation and creates barrier at lid margin
35
What is responsible for the autonomic control of the production and distribution of tears?
```
CN V (Trigeminal Nerve) - Lacrimal Nerve - sympathetic and parasympathetic (get both at pterygopalatine ganglion)
CN VII (Facial Nerve) - Parasympathetic
```
36
What is the process of tear drainage?
Aqueous tear film moved into palpebral fissure
Swept into medial canthus
Into Lacrimal puncti (dorsal and ventral)
These lead into canaliculi
Lacrimal canaliculi empty into nasolacrimal duct
37
In a normal/dog shaped dog (thanks for that Alison...), where does the nasolacrimal duct drain into?
Medial part of Nasal Punctum (it's in the dogs nostril)
38
In cats and brachycephalic dog breeds, where does the nasolacrimal duct drain into?
Caudal nasopharynx. Can be checked using dye and looking at the back of the mouth
39
How is the lacrimal drainage system in the rabbit vulnerable?
Only one lacrimal puncta.
Runs over cheek teeth.
Reserved crown can lead to blockage of lacrimal puncta.
Also two sharp bends in the nasolacrimal duct/canaliculi so easily blocked
40
Where is the lacrimal caruncle, in the eye of a horse?
Medial canthus
41
Where are the Meibomian/tarsal glands found?
In the tarsal plate (in the eyelid)
42
Damage to which cranial nerves will result in loss of the palpebral reflex?
Loss of the reflex can be down to two things. Either the animal can't feel or it can't blink.
If it can't feel - sensory - trigeminal nerve (CN V)
If it can't blink - motor - facial nerve (CN VII)
43
What are the layers of the globe?
Fibrous layer - sclera and cornea
Vascular layer - Uvea (Iris, lens etc)
Neural layer - retina
44
How can the globe be divided?
The merideans dorsally and ventrally
| The equator rostrally and caudally
45
What are the internal compartments of the globe?
The anterior segement (further subdivided by the iris) - everything in front of the lens
- anterior chamber = in front of the iris
-posterior chamber = behind the iris
The posterior segment - everything behind the lens
46
How does the cornea get nutrition?
Tear fill and aqueous humour. It's avascular
47
what is curved and should be completely transparent, with a slight refracting function?
The cornea
48
What is the name of the region where blood vessels terminate in the eye?
Corneoscleral limbus - the junction between the cornea and the sclera
49
What are the layers of the cornea (from most external to most internal)?
Anterior epithelium
Stroma
Descemet's membrane
Endothelium
50
What type of epithelium makes up the anterior epithelium?
Squamous to columnar
51
What are features of the stroma?
Thickest part of the cornea
Lamellae of collagen fibrils - relatively dehydrated as water disrupts the structure
Keratocytes - can become fibroblasts if injured
Proteoglycans & GAGs
52
How can the structure of the stroma be disrupted and why is this significant?
The stroma is relatively dehydrated and any water entering it will disrupt the structure of the lamallae.
Any disruption the lamallae leads to a loss of transparency
53
Which layer of the cornea is produced by the endothelium and thickens with age?
Descemet's membrane
54
What is the function of the endothelium?
Produces Descemet's membrane
Maintains stromal dehydration - pumps out water
Can't regenerate in most mammalian species. Heals by cells spreading out. Can't replace cells except in rabbits.
Damage leads to cloudiness, also means aqueous humour can leak in
55
Why is superficial damage to the cornea more painful than deep damage?
The cornea is heavily innervated by CN V (trigeminal nerve).
Pain fibres are mostly in the anterior epithelium (message to stop poking yourself in the eye).
Pressure receptors mainly in the stroma (still has some pain receptors but far fewer than in AE
56
What is a bletherospasm?
Holding eye shut (because it's painful)
57
How might a fluoroscene dye display differently on a superficial corneal ulcer to a deep corneal ulcer?
Fluoroscene dye will stick to the stroma in a superficial ulcer resulting in a fluorescent colouring.
In a deep ulcer where the stroma is gone and Descemet's membrane is exposed, no stain will be picked up because the stroma is gone.
58
What is a descemeticile?
Ulcer when it is just the Descemet's membrane is stopping the eyeball from bursting
59
What is a corneal oedema?
Opacity due to water moving into the eye
60
What is the difference between a corneal oedema and cataracts?
a corneal oedema happens when there is water in the cornea (iris and pupil appears clouded).
Cataracts is cloudiness in the lens (so only the pupil will appear clouded)
61
What is corneal neovascularisation?
Growth of blood vessels to facilitate damage repair
62
What is superficial neovascularisation?
Blood vessel branches grow inward from conjunctiva. Will later recede but not entirely, leaving ghost vessels behind
63
What is deep neovascularisation?
Blood vessels grow from ciliary body blood vessels/deeper structures of the eye.
Implies deeper damage
64
What sort of tissue makes up the sclera?
tough fibrous tissue. bouncy and springy (Alisons words)
65
What is the exception that prevents the sclera being a complete structure, and why?
The lamina cribosa is a perforated plate which allows axons of the optic nerve to exit the eye
66
What colour is the sclera?
Normally white, although can change with age. Thinner sclera whilst young can result in it appearing blue due to iris pigment showing through it. Can also appear a more ivory colour with age. Should never be yellow (jaundice)
67
How do the sclera of birds and lizards differ to that of mammals?
There is bone within their sclera - ossicles.
| ossicles extended in hawks and owls - hold eye out of the skull
68
Does the sclera have it's own blood supply?
Blood supplied via the episclera - highly vascular and is confluent with the fascia bulbi
69
When the eye is red and inflamed and blood vessels are visible, how do you differentiate between episcleral and conjunctival blood vessels?
Normally vasodilation of conjunctiva is responsible.
Very straight blood vessels are more likely to be episcleral
Indicative of deeper damage
Give constrictors if unsure (adrenoreceptor agonist or adrenaline substitute)
70
What makes up the uvea?
iris, ciliary body, choroid
71
What makes up the anterior uveal tract?
Iris and ciliary body
72
What makes up the posterior uveal tract?
choroid
73
What is the function of the iris?
Controls light entry to posterior segment
Alters depth of light focus
Varies in shape between species
74
What are the layers of the iris?
Anterior border layer
Stroma
Posterior (pigmented) Epithelium
75
What muscles are involved in iris movement?
Constrictor muscle - in stroma of pupillary zone (parasympathetic innervation CN III - constricts pupil)
Dilator muscle - from sphincter to periphery (sympathetic innervation - widens pupil)
Muscles striated in non-mammalian species
76
What separates the pupillary and ciliary zones?
the collarette
77
Why does the horse have an oval shaped cornea and pupil?
Wider view/panoramic view. Better for scanning horizon for predators
78
What are the granula iridica?
Small round pigmented masses seen at the pupillary margin. They improve the efficiency of pupil constriction. Outgrowths of the posterior epithelium of iris that project out into pupil
79
What is the correct term for pupil constriction?
Miosis
80
What is the correct term for pupil dilation?
Mydriasis
81
What determines the shape of the pupil?
The shape of the constrictor muscle. e.g in the cat the muscle goes dorsal to ventral and interlaces around the pupil (medial to lateral in ungulates)
82
How is the iris attached?
The iris is attached at root to the ciliary body
83
What is the function of the ciliary body?
produces aqueous humour (is also involved in draining aqueous humour)
suspends the lens using zonular fibres
has a non pigmented layer acting as a barrier between vascular tissue and aqueous humour AKA blood ocular barrier
84
How does the ciliary body allow the lens to change shape?
Zonular fibres are attached to projections called ciliary processes.
Muscles at the base of the ciliary processes contracts, allowing the lens to change shape - varying ability to do this.
In non-mammalian species, they attach directly to the lens - no zonary fibres
85
Function of the iridiocorneal angle?
contains a meshwork of pectinate ligaments underneath which aqueous humour can drain through - results in glaucoma if can't drain
86
What are the 4 layers of the choroid, and what are their features/functions?
```
Suprachoroidea - outermost
- heavily pigmented and elastic
Large vessel layer
- cools the eye - venous plexus
Medium vessel layer
- contains tapetum lucidum (needed for low light - reflects light back on photoreceptors)
-vessels link with choriocapillaris
Choriocapillaris
- fenestrated capillaries
-supplies retina
```
87
What is the function of aqueous humour?
Provides nutrition to lens and cornea
Maintains IOP
Constant drainage and production
88
Aqueous humuor is produced by the ciliary processes through which methods?
Diffusion
Ultrafiltration
Active secretion = main method
89
How is lost sodium replaced by the epithelium?
Pumping bicarbonate ions into the aqueous humour
90
What is the conventional pathway for aqueous humour drainage?
Drains at iridocorneal angle, across pectinate ligaments, through trabecular meshwork of ciliary cleft, through aqueous plexus, to scleral venous plexus, and into vortex veins
91
How does the unconventional or uveoscleral pathway differ to the conventional pathway and why is it important?
The unconventional pathway bypasses the aqueous plexus. This becomes important in glaucoma cases (as if production > drainage = glaucoma)
92
The vitreous humour is...
...jelly like hydrogel containing fibrils of protein and hyaluronic acid - arranged to maintain clarity
...contained in the posterior segment
...not a static structure
...attached to lens, ciliary body, and margins of the optic disc
93
What is the function of the vitreous humour?
transmits light
stores nutrients and waste products
lends physical support
94
What are floaters?
Precipitations of hyaluronic acid - can be seen on opthalmoscopy of older animals
95
What is the function of the lens?
Focuses light on the retina - relies on transparency, stable position, and ability to change shape
96
How is the lens held in place?
suspended by zonular fibres from ciliary processes
97
Name 4 parts of the lens
```
Capsule
Cortex of lens fibres
Nucleus - gets bigger with age (can also appear cloudier but light still goes through it - unlike cataracts)
Anterior epithelium
- maintains dehydration
- produces lens fibres
```
98
What are the observable differences between cataracts and nuclear sclerosis?
Despite appearing cloudier, light will still pass through a lens with nuclear sclerosis. It won't in cataracts
In addition cataracts often starts at the sutures
99
What is the fundus and what does it consist of?
The fundus is part of the posterior segment viewed with an opthalmoscope
consists of
-optic disc
-retina & RPE (retinal pigmented epithelium)
- choroid
- sclera
100
Within the retina, the area centralis is...
the area with the most cones
101
Within the retina, the visual streak is...
the area with the most ganglion cells
102
Why are the axons of the retina not myelinated?
to allow light to reach the photoreceptors
103
What does the retinal pigmented epithelium overlie?
choriocapillaris
104
What is unusual about the retinal pigmented epithelium when it is over the tapetum?
It is non-pigmented
105
How will a detached retina appear when viewed using an opthalmoscope?
retina and blood vessels will be hanging forward when they should usually be flat. If the retina is completely detached the animal will be totally blind!
106
How does the fundus of the dog and cat differ?
The optic disc of the cat appears rounder and darker, whereas the dogs is lighter and can appear almost triangular. Axons are also myelinated earlier?
107
What is unusual about a rabbit fundus?
Has blood vessels and myelinated axons
108
What is unusual about the fundus of the horse and the guinea pig?
Lots of little blood vessels terminating. Known as the stars of Wimslow
109
What is unusual about the fundus of a bird?
The presence of an infolding of choroid called the pectin. It's pigmented
